Q on kiln wiring

[ag001]

I'm in the process of setting up my studio (finally!) after a move. I have two kilns, a Cress E1814 with a 6-30P and a Skutt KM1027 with a 15-50P. I understand the Cress will need a 30A breaker with #8 wire and the Skutt will need a 60A breaker with #6 wire.

With limited space in the panel, is it possible to install only a 60A breaker and #6 wire, switching the plug on the smaller Cress kiln? I understand why I can't go the other way, but am not sure why this wouldn't work...  Any thoughts would be very appreciated. I will find a good kiln electrician to help me, but I'd like to have a bit of knowledge before I do.

[Mark_H]

Yes you can run wire big enough to serve both loads (and the voltage drop distance and temperature/ampacity de-rating of wire) and then each kiln would have separate disconnects/fuse/breakers of the appropriate size.

There is also a ‘tap rule’ within so many feet that can save some money (check the NEC).  Typical commercial is staying below 80% of the breaker rating, but the code allows multiple percentages and often requires oversizing  of conductors based on application.

I’d call a sparky that does commercial work as kilns are not typical residential faire, and the would likely be more familiar with specific code sections that can save money. 

[Dick White]

Hmm, it's not computing for me. The Cress draws 24 amps at 240V single phase (or 23 amps on commercial 208V single phase service) and thus under the 125% rule needs to be on a 3-wire 30 amp circuit with a 6-30R  receptacle to match the 6-30P plug on the kiln. If the Skutt has a 15-50P plug, that means it's a 4-wire 3-phase device, which is incompatible with the single phase Cress. The two circuits are fundamentally different.

If the Skutt is actually single phase and uses a 6-50 plug and receptacle on a 240V (or 208V commercial) 60 amp circuit, you still can't get there from here. A kiln should be on a circuit that is sized at 125% of the nominal rating of the kiln, but the circuit should not be fused at more that 150% of the kiln rating. Thus, the 24 amp  Cress should not be on a circuit that is more than 40 amps.

[Mark C.]

Dick is spot on-cannot do both safely-have the electrician run two plugs with two breakers and two wire sizes. If you need curcuit box space have them put some twin breakers in for more space for the doubles .

[neilestrick]

First, I've never seen a Skutt 1027 set up for a 4 wire power cord. Typically a Skutt would have a 6-50 plug, which is a 3 wire setup- 3 hots and a ground. I'm wondering if someone put a 15-50 on it but they didn't use the neutral. Double check the wiring in the kiln control box and see what they actually did, but I'd swap it out for a proper 6-50 plug to avoid any future confusion.

You cannot run the smaller kiln on the 60 amp circuit. It's not safe. However if you've only got one slot in your main panel, you can run a subpanel off that one slot, then have the two kiln circuits come off that subpanel. If you've got enough available amperage, the subpanel could be 100 amps and you could run both kilns at the same time. Otherwise you can do a 60 amp subpanel and just run one kiln at a time.

[Dick White]

1 hour ago, neilestrick said:

First, I've never seen a Skutt 1027 set up for a 4 wire power cord.

A 1027 built for a 3-phase installation has the 4-wire 15-50 plug. Even if the amperages were compatible, it would be real kludge to be running the single phase Cress using only 2 of the prongs on a 3-phase receptacle.

[ag001]

5 hours ago, Dick White said:

Hmm, it's not computing for me. The Cress draws 24 amps at 240V single phase (or 23 amps on commercial 208V single phase service) and thus under the 125% rule needs to be on a 3-wire 30 amp circuit with a 6-30R  receptacle to match the 6-30P plug on the kiln. If the Skutt has a 15-50P plug, that means it's a 4-wire 3-phase device, which is incompatible with the single phase Cress. The two circuits are fundamentally different.

If the Skutt is actually single phase and uses a 6-50 plug and receptacle on a 240V (or 208V commercial) 60 amp circuit, you still can't get there from here. A kiln should be on a circuit that is sized at 125% of the nominal rating of the kiln, but the circuit should not be fused at more that 150% of the kiln rating. Thus, the 24 amp  Cress should not be on a circuit that is more than 40 amps.

I really appreciate all of the advice here. And apologies, I thought I replied earlier but for some reason it didn’t go through. 
 

You are correct, the skutt is indeed a single phase with the 6-50 plug. I think I must have copied the wrong row on their site. 
 

I didn’t realize I might be able to do a 60A subpanel. That would be perfect I think. The entire panel is only 100A  and has a fair load on it already, so my plan already was to only run one at a time and not have anything else running at the same time. 

[Mark C.]

Have an electrician run a sub panel to kiln area and put in a 60 amp plug  with breaker and 40 amp plug  with breaker from sub panel. Since if you only have 100 amps at home you will be paying attention to whats on anyway during a firing.

If your main panel is full  you can use a few twins (they fit one slot and hold two breakers ) to free up a double slot for that twin sub panel breaker

[neilestrick]

3 hours ago, Dick White said:

A 1027 built for a 3-phase installation has the 4-wire 15-50 plug. Even if the amperages were compatible, it would be real kludge to be running the single phase Cress using only 2 of the prongs on a 3-phase receptacle.

Sorry, I was assuming it was a single phase kiln.

[Dick White]

3 minutes ago, neilestrick said:

Sorry, I was assuming it was a single phase kiln.

He has corrected his information, it is a single phase with a 6-50 plug.

[Pyewackette]

I have a related question.  I'm looking at getting the L&L e18S-3.

It runs on 24A, requires a 30A breaker and 10G wire, yet has a NEMA 6-50 plug with optional 6-30 or 10-30 cords available according to this diagram.

NEMA 6-50 is 250V 3 wire 2 pole 50A - 2 hots and a ground

NEMA 6-30 is 250V 3 wire 2 pole 30A - 2 hots and a ground

NEMA 10-30 is 125/250V 3 wire 3 pole 30A - 2 hots and a ground - Older dryer connection?

NEMA 14-30 (which is my dryer receptacle) is 125/250V 4 wire 3 pole 30A - 2 hots, a ground, and neutral?  New dryer connection.

So questions are:

1. Why do they put a 50A plug on a 24A draw/30A breaker kiln as default?
2. What is the difference between 2 and 3 poles in this context?
3. What is the difference between 125/250V and 250V?
4. Given that my current dryer receptacle is using 10G wire, which it should be if it is to code, can I just swap the receptacle mounted in the wall (since I don't own a dryer and don't plan to), vent the kiln out the dryer vent to go out through the roof, and call it a day?
5. And if so, which receptacle/cord combination should I choose?

Actually there is one more question but I'm pretty sure there's a good reason for NOT doing this - why isn't 14-30 a choice for the cord, wouldn't the wiring of the kiln just ignore the neutral?

[neilestrick]

2 hours ago, Pyewackette said:

Why do they put a 50A plug on a 24A draw/30A breaker kiln as default?

It makes production easier and inventory simpler. However they do offer other cords see HERE.

2 hours ago, Pyewackette said:

What is the difference between 2 and 3 poles in this context?

2 pole is single phase (2 hots), 3 pole is 3 phase (3 hots), generally only available for commercial spaces.

2 hours ago, Pyewackette said:

What is the difference between 125/250V and 250V?

125/250 means it's a 4 wire setup with 2 hots, a neutral , and a ground. It's used when part of the system needs to run on 120 volts (needs the neutral) instead of the full 240 volts. Like if you have a kitchen oven or clothes dryer where the heating part uses 240 volts, but the control panel only needs 120 volts. In a kiln it's used in 18"x18" kilns where the two 9" sections are run on separate 120 volt lines.

 

2 hours ago, Pyewackette said:

Given that my current dryer receptacle is using 10G wire, which it should be if it is to code, can I just swap the receptacle mounted in the wall (since I don't own a dryer and don't plan to), vent the kiln out the dryer vent to go out through the roof, and call it a day?

As long as everything on the circuit (plugs, outlets, wiring, etc) are rated to handle the amperage of the breaker on the circuit, you're good to go. So yes, swap out the receptacle and you're good.

2 hours ago, Pyewackette said:

And if so, which receptacle/cord combination should I choose?

I'd stick with the 6-50 that comes standard on the kiln, because it's over-rated and will likely last longer.

[Pyewackette]

4 minutes ago, neilestrick said:

2 pole is single phase (2 hots), 3 pole is 3 phase (3 hots), generally only available for commercial spaces.

Well that is what I thought but then both new and old dryer cords are apparently 3 pole (3 phase) according to this.  14-30 and 10-30 both say 3 pole on that chart.  Those are standard dryer cords (or used to be in the case of the 10-30) but they say they are 3 phase and we wouldn't have 3 phase in a residence. So I guess I still don't understand the nomenclature or what is actually going on with that.

I had thought there was some difference to do with the way they implement the 240V, they sort of stack it on the ones that are 125v/250v and they run them "simultaneously" if its 250v.  I'm pretty sure that's not correct electricalese but hopefully my pig-electricalese is close enough ...

So its the addition of the  neutral on the 14-30 that makes it not work with the kiln?  Because old dryer cord without the neutral still works (since they will provide a 10-30 cord). I had hoped that was wiring in the device but apparently there's some connection within the receptacle itself? EG it DOESN'T just get ignored via not having specific wiring to connect to that prong? I used to just swap dryer cords in the olden days and the dryers still seemed to work regardless of the receptacle, thought the neutral just got ignored by devices that didn't need it. My last dryer was pushing 50 and still worked so it had its cord swapped several times.

[neilestrick]

7 minutes ago, Pyewackette said:

Well that is what I thought but then both new and old dryer cords are apparently 3 pole (3 phase) according to this.  14-30 and 10-30 both say 3 pole on that chart.  Those are standard dryer cords (or used to be in the case of the 10-30) but they say they are 3 phase and we wouldn't have 3 phase in a residence. So I guess I still don't understand the nomenclature or what is actually going on with that.

Poles refers to the number of poles on the breaker switch. 3 pole means a triple breaker for 3 phase service. A 4 wire cord would be used as 3 phase plus a ground, or as single phase 120/240 (2 hots, neutral, ground).

32 minutes ago, Pyewackette said:

So its the addition of the  neutral on the 14-30 that makes it not work with the kiln?  Because old dryer cord without the neutral still works (since they will provide a 10-30 cord). I had hoped that was wiring in the device but apparently there's some connection within the receptacle itself? EG it DOESN'T just get ignored via not having specific wiring to connect to that prong? I used to just swap dryer cords in the olden days and the dryers still seemed to work regardless of the receptacle, thought the neutral just got ignored by devices that didn't need it. My last dryer was pushing 50 and still worked so it had its cord swapped several times.

You can use a 4 wire cord, but the neutral wouldn't be hooked up. As a repair person I really hate when that is done, because the plug doesn't match up with what the serial plate says, and I have to open up the  control box and figure out what's going on. In some kilns it can be a lot of work to get to the power cord in the control box because it's often hidden behind an insulating baffle.

[Mark_H]

15 hours ago, Mark C. said:

Have an electrician run a sub panel to kiln area and put in a 60 amp plug  with breaker and 40 amp plug  with breaker from sub panel. Since if you only have 100 amps at home you will be paying attention to whats on anyway during a firing.

If your main panel is full  you can use a few twins (they fit one slot and hold two breakers ) to free up a double slot for that twin sub panel breaker

I think Mark's suggestion here is the best idea.  It's the same idea as running a large branch circuit with separate fuse-able disconnects to each kiln, but would be cheaper as you can use the breakers in the sub-panel as disconnects (switches) as long as they're rated for switching and if they are in view/distance requirements of the kilns.  It would also allow for future 120vac receptacles nearby.  Here's some more info on the tap rule if you are interested.  It might save you putting in a sub panel main breaker, if your conditions are applicable.  https://www.ecmag.com/section/codes-standards/applied-tap-ruleshttps://www.ecmag.com/section/codes-standards/applied-tap-rules

 

[Pyewackette]

@neilestrick I see now.  Thanks for satisfying my curiosity.  On the dryer the connections for the cord were really easy to get to so of course that made swapping the cords in and out trivial.

It appears that the receptacle for 6-50 is cheap enough and I should be able, actually, to install that myself. That's the same receptacle the Big Ceramic Store sells for small kilns, only about a quarter of the cost. That'll save me about $180 over buying a cord from L&L, too, LOL! 

I can tell what gauge the wire is once I take the faceplate off the receptacle and while it SHOULD be 10g, I'll make sure that it actually IS 10g.  The receptacle itself is only about 8' - 10' from the breaker box so its a short run.  For this sort of thing if I were installing new wire I'd go up a gauge (as in heavier duty) but it should be fine for this.  It's a pretty small kiln and will most often be used at very low heat for burnishing anyway.  It will only be run at higher temps when testing glazes and kiln bodies, which I probably won't even bother to try until supply chain stuff works itself out, what with changes in talc and other supplies that are in flux right now.

All I should have to do is cap off the neutral and make sure the hots go to hots and the ground wire goes to the ground on the receptacle.

Thanks.

[Mark C.]

Just a note about the -Big Ceramic Store is long closed up  now and was doing bad things to customers when it went sideways and crashed

[Pyewackette]

@Mark C. Oh its THAT one.  I forgot.  I'm familiar with them.  And not in a good way.  It does explain offering a common electrical part at 4x the going rate though LOL!

[neilestrick]

You can get a 6-50 receptacle at just about any hardware store for $15-20.

[Pyewackette]

38 minutes ago, neilestrick said:

You can get a 6-50 receptacle at just about any hardware store for $15-20.

$8 at Home Despot LOL!

[Mark C.]

3 hours ago, Rockhopper said:

Whether this is an option depends on the physical size and current rating of the panel.  Some will accept 'twins' in all slots,  some in only a few slots, and other not at all.  (The label on the panel should tell you how many circuits it can hold - and which breakers are approved for use in that panel.)

There are so-called 'universal' breakers on the market that might be able to get around the limitations built into the panel by the manufacturer but, unless something has changed since I last looked at a code-book, using one to exceed the maximum number of circuits listed is a code violation - and potentially dangerous, as they may not fit properly in a panel that isn't designed for them.

All true-I usually use twins in lighting curcuts  usually (15 amp low draw). I many older homes with older obscure panels like Bulldog brand or others twins do not exist. Even older style cuttler hammer  boxes twins are hard to find. The newer cuttler style boxes  twins are an easy find.

If the home is maxed out at 100 amps then really new service panel upgrade  is whats needed.

I did that at our place in the 80s and bumped it up to 200 amp service panel..Of course with 220 well and a pot shop with electrics it all made since .

I wish back then I had gotten a different panel as this one is to narrow.

Now its stuffed because of my standby generator with its own panel that uses the connections in 200 amp panel as well as some 220 heat pumps and a solar connection.Less breakers being used but more connections in same box